Basic knowledge of developmental biology and behavior science is essential to the understanding of the normal and abnormal development of man. The process by which genetic information is translated through differentiation and organization into the complex structure of the differentiated organism is one of the most important problems facing the biologist today. The Developmental Biology program established in 1962 as a priority research division of the Department of Pediatrics and now a part of the Child Development and Mental Retardation Center is composed of a group of senior investigators representing several different disciplines (enzymology, biochemistry, behavioral science, genetics, embryology, steroid chemistry, immunology) who, working individually and in collaboration, are interested in problems relating to human and mammalian cellular and embryonic growth, development and differentiation. The problems presently under study are: the etiology of congenital malformations and mental retardation, the development of immunological mechanisms in the embryo, studies of the development of the nervous system, studies of mitochondrial development, structure, function and origin, studies of preimplantation, and studies of the development and differentiation processes in human somatic cells in tissue culture. In the proposed program eight senior investigators are submitting five distinct but related research projects in the area of developmental biology and behavioral science to be performed by both collaborative and individual efforts.